DOCSLIB.ORG

K–T Boundary

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
K–T Boundary K–T boundary From Wikipedia, the free encyclopedia (Redirected from Kt boundary) The K-T boundary is a geological signature, usually a thin band, dated to 65.5 ± 0.3 (mya).[1] K is the traditional abbreviation for the Cretaceous Period, and T is the abbreviation for the Tertiary Period. The boundary marks the end of the Mesozoic Era, and the beginning of the Cenozoic Era, and is associated with the Cretaceous–Tertiary extinction event, a mass extinction.[2] Contents Badlands near Drumheller, Alberta where erosion 1 Possible causes has exposed the KT boundary. 1.1 Alvarez impact hypothesis 1.2 Chicxulub Crater 1.3 Deccan Traps 1.4 Multiple impact event 1.5 Maastrichtian sea-level regression 1.6 Supernova hypothesis 2 Footnotes Possible causes Alvarez impact hypothesis In 1980, a team of researchers consisting of Nobel prize-winning physicist Luis Alvarez, his son, geologist Walter Alvarez, and chemists Frank Asaro and Helen Michels discovered that sedimentary layers found all over the world at the Cretaceous– Tertiary boundary contain a concentration of iridium many times greater than normal (30 times and 130 times background in the two sections originally studied). Iridium is extremely rare in the earth's crust because it is a siderophile, and therefore most of it travelled with the iron as it sank into the earth's core during planetary differentiation. As iridium remains abundant in most asteroids and comets, the Alvarez team suggested that an asteroid struck the earth at the time of the K–T boundary.[3] There were other earlier speculations on the possibility of an The K–T boundary impact event, but no evidence had been uncovered at that exposure in time.[4] Trinidad Lake State Park, in the Raton Basin of The evidence for the Alvarez impact theory is supported by Colorado, USA, chondritic meteorites and asteroids which have an iridium shows an abrupt [5] change from dark concentration of ~455 parts per billion, much higher than ~0.3 to light colored parts per billion typical of the earth's crust.[3] Chromium isotopic rock. White line added to mark the anomalies found in Cretaceous–Tertiary boundary sediments are transition. similar to that of an asteroid or a comet composed of carbonaceous chondrites. Shocked quartz granules and tektite glass spherules, indicative of an impact event, are also common in the K–T boundary, especially in deposits from around the Caribbean. All of these constituents are embedded in a layer of clay, which the Alvarez team interpreted as the debris spread all over the world by the impact.[3] Using estimates of the total amount of iridium in the K–T layer, and assuming that the asteroid contained the normal percentage of iridium found in chondrites, the Alvarez team went on to calculate the size of the asteroid. The answer was about 10 kilometers (6 mi) in diameter, about the size of Manhattan.[3] Such a large impact would have had approximately the energy of 100 trillion tons of TNT, or about 2 million times greater than the most powerful thermonuclear bomb ever tested. The obvious consequence of an impact would be a dust cloud which would block sunlight and inhibit photosynthesis for a few years. This would account for the extinction of plants and phytoplankton and of organisms dependent on them (including predatory animals as well as herbivores). However, small creatures whose food chains were based on detritus might have still had a reasonable chance of survival. It is estimated that sulfuric acid aerosols were injected into the stratosphere, leading to a 10–20% reduction in sunlight reaching the earth's surface. It would have taken at least ten years for those aerosols to dissipate.[6][7] Global firestorms may have resulted as incendiary fragments from the blast fell back to Earth. Analyses of fluid inclusions in ancient amber suggest that the oxygen content of the atmosphere was very high (30–35%) during the late Cretaceous. This high O2 level would have supported intense combustion. The level of atmospheric O2 plummeted in the early Tertiary Period. If widespread fires occurred, they would have increased the CO2 content of the atmosphere and caused a temporary greenhouse effect once the dust cloud settled, and this would have exterminated the most vulnerable survivors of the "long winter".[6] The impact may also have produced acid rain, depending on what type of rock the asteroid struck. However, recent research suggests this effect was relatively minor. Chemical buffers would have limited the changes, and the survival of animals vulnerable to acid rain effects (such as frogs) indicate this was not a major contributor to extinction. Impact theories can only explain very rapid extinctions, since the dust clouds and possible sulphuric aerosols would wash out of the atmosphere in a fairly short time—possibly under ten years.[8] Chicxulub Crater When it was originally proposed, one issue with the "Alvarez hypothesis" (as it came to be known) had been that no documented crater matched the event. This was not a lethal blow to the theory; since although the crater resulting from the impact would have been larger than 250 kilometers (155 mi) in diameter, Earth's geological processes hide or destroy craters over time.[9] Subsequent research, however, identified the Chicxulub Crater buried under Chicxulub on the coast of Yucatan, Mexico as the impact crater which matched the Alvarez hypothesis dating. Identified in 1990 based on the work of Glen Penfield done in 1978, this crater is oval, with an average diameter of about 180 kilometers (112 mi), about the size calculated by the Alvarez team.[10] Radar topography reveals the The shape and location of the crater indicate further causes of devastation in 180 kilometers (112 mi) wide addition to the dust cloud. The asteroid landed right on the coast and would have ring of the crater. caused gigantic tsunamis, for which evidence has been found all round the coast of the Caribbean and eastern United States—marine sand in locations which were then inland, and vegetation debris and terrestrial rocks in marine sediments dated to the time of the impact. The asteroid landed in a bed of gypsum (calcium sulphate), which would have produced a vast sulphur dioxide aerosol. This would have further reduced the sunlight reaching the earth's surface and then precipitated as acid rain, killing vegetation, plankton and organisms which build shells from calcium carbonate (coccolithophorids and molluscs). The crater's shape suggests that the asteroid landed at an angle of 20° to 30° from horizontal and traveling north-west. This would have directed most of the blast and solid debris into the central part of what is now the United States. Most paleontologists now agree that an asteroid did hit the Earth about 65 mya, but there is an ongoing dispute whether the impact was the sole cause of the extinctions.[9][11] Gerta Keller suggests that the Chicxulub impact occurred approximately 300,000 years before the K–T boundary. This dating is based on evidence collected in Northeast Mexico, detailing multiple stratigraphic layers containing impact spherules, the earliest of which occurs approximately 10 meters (33 ft) below the K–T boundary. This chronostratigraphic sequence of rock is thought to represent 300,000 years. This finding supports the theory that one or many impacts were contributory, but not causal, to the K–T boundary mass extinction.[9] However, many scientists reject Keller's analysis, some arguing that the 10 meter (32.8 ft) layer on top of the impact spherules should be attributed to tsunami activity resulting from impact. Few researchers support Keller's dating of the impact crater.[11] Deccan Traps Before 2000, arguments that the Deccan Traps flood basalts caused the extinction were usually linked to the view that the extinction was gradual, as the flood basalt events were thought to have started around 68 mya and lasted for over 2 million years. However, there is evidence that two-thirds of the Deccan Traps were created in 1 million years about 65.5 mya, so these eruptions would have caused a fairly rapid extinction, possibly a period of thousands of years, but still a longer period than what would be expected from a single impact event.[12][13] The Deccan Traps could have caused extinction through several mechanisms, including the release of dust and sulphuric aerosols into the air which might have blocked sunlight and thereby reducing photosynthesis in plants. In addition, Deccan Trap volcanism might have resulted in carbon dioxide emissions which would have increased the greenhouse effect when the dust and aerosols cleared from the atmosphere.[13] In the years when the Deccan Traps theory was linked to a slower extinction, Luis Alvarez (who died in 1988) replied that paleontologists were being misled by sparse data. While his assertion was not initially well-received, later intensive field studies of fossil beds lent weight to his claim. Eventually, most paleontologists began to accept the idea that the mass extinctions at the end of the Cretaceous were largely or at least partly due to a massive Earth impact. However, even Walter Alvarez has acknowledged that there were other major changes on Earth even before the impact, such as a drop in sea level and massive volcanic eruptions that produced the Indian Deccan Traps, and these may have contributed to the extinctions.[14] Multiple impact event Several other craters also appear to have been formed about the time of the K–T boundary. This suggests the possibility of near simultaneous multiple impacts, perhaps from a fragmented asteroidal object, similar to the Shoemaker-Levy 9 cometary impact with Jupiter. Among these are the Boltysh crater, a 24 kilometers (15 mi) diameter impact crater in Ukraine (65.17 ± 0.64 mya); and the Silverpit crater, a 20 kilometers (12 mi) diameter impact crater in the North Sea (60–65 mya).
Load more

Recommended publications
  • South Dakota to Nebraska
    Geological Society of America Special Paper 325 1998 Lithostratigraphic revision and correlation of the lower part of the White River Group: South Dakota to Nebraska Dennis O. Terry, Jr. Department of Geology, University of Nebraska—Lincoln, Lincoln, Nebraska 68588-0340 ABSTRACT Lithologic correlations between type areas of the White River Group in Nebraska and South Dakota have resulted in a revised lithostratigraphy for the lower part of the White River Group. The following pedostratigraphic and lithostratigraphic units, from oldest to youngest, are newly recognized in northwestern Nebraska and can be correlated with units in the Big Badlands of South Dakota: the Yellow Mounds Pale- osol Equivalent, Interior and Weta Paleosol Equivalents, Chamberlain Pass Forma- tion, and Peanut Peak Member of the Chadron Formation. The term “Interior Paleosol Complex,” used for the brightly colored zone at the base of the White River Group in northwestern Nebraska, is abandoned in favor of a two-part division. The lower part is related to the Yellow Mounds Paleosol Series of South Dakota and rep- resents the pedogenically modified Cretaceous Pierre Shale. The upper part is com- posed of the unconformably overlying, pedogenically modified overbank mudstone facies of the Chamberlain Pass Formation (which contains the Interior and Weta Paleosol Series in South Dakota). Greenish-white channel sandstones at the base of the Chadron Formation in Nebraska (previously correlated to the Ahearn Member of the Chadron Formation in South Dakota) herein are correlated to the channel sand- stone facies of the Chamberlain Pass Formation in South Dakota. The Chamberlain Pass Formation is unconformably overlain by the Chadron Formation in South Dakota and Nebraska.
    [Show full text]
  • Asteroid Impact, Not Volcanism, Caused the End-Cretaceous Dinosaur Extinction
    Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction Alfio Alessandro Chiarenzaa,b,1,2, Alexander Farnsworthc,1, Philip D. Mannionb, Daniel J. Luntc, Paul J. Valdesc, Joanna V. Morgana, and Peter A. Allisona aDepartment of Earth Science and Engineering, Imperial College London, South Kensington, SW7 2AZ London, United Kingdom; bDepartment of Earth Sciences, University College London, WC1E 6BT London, United Kingdom; and cSchool of Geographical Sciences, University of Bristol, BS8 1TH Bristol, United Kingdom Edited by Nils Chr. Stenseth, University of Oslo, Oslo, Norway, and approved May 21, 2020 (received for review April 1, 2020) The Cretaceous/Paleogene mass extinction, 66 Ma, included the (17). However, the timing and size of each eruptive event are demise of non-avian dinosaurs. Intense debate has focused on the highly contentious in relation to the mass extinction event (8–10). relative roles of Deccan volcanism and the Chicxulub asteroid im- An asteroid, ∼10 km in diameter, impacted at Chicxulub, in pact as kill mechanisms for this event. Here, we combine fossil- the present-day Gulf of Mexico, 66 Ma (4, 18, 19), leaving a crater occurrence data with paleoclimate and habitat suitability models ∼180 to 200 km in diameter (Fig. 1A). This impactor struck car- to evaluate dinosaur habitability in the wake of various asteroid bonate and sulfate-rich sediments, leading to the ejection and impact and Deccan volcanism scenarios. Asteroid impact models global dispersal of large quantities of dust, ash, sulfur, and other generate a prolonged cold winter that suppresses potential global aerosols into the atmosphere (4, 18–20). These atmospheric dinosaur habitats.
    [Show full text]
  • Exceptionally Well-Preserved Fossils in a Middle Ordovician Impact Crater
    Downloaded from http://jgs.lyellcollection.org/ by guest on September 29, 2021 Review focus Journal of the Geological Society Published Online First https://doi.org/10.1144/jgs2018-101 The Winneshiek biota: exceptionally well-preserved fossils in a Middle Ordovician impact crater Derek E.G. Briggs1,2*, Huaibao P. Liu3, Robert M. McKay3 & Brian J. Witzke4 1 Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA 2 Yale Peabody Museum of Natural History, Yale University, New Haven, CT 06520, USA 3 Iowa Geological Survey, IIHR – Hydroscience & Engineering, University of Iowa, 340 Trowbridge Hall, Iowa City, IA 52242, USA 4 Department of Earth and Environmental Sciences, University of Iowa, 115 Trowbridge Hall, Iowa City, IA 52242, USA D.E.G.B., 0000-0003-0649-6417 * Correspondence: [email protected] Abstract: The Winneshiek Shale (Middle Ordovician, Darriwilian) was deposited in a meteorite crater, the Decorah impact structure, in NE Iowa. This crater is 5.6 km in diameter and penetrates Cambrian and Ordovician cratonic strata. It was probably situated close to land in an embayment connected to the epicontinental sea; typical shelly marine taxa are absent. The Konservat-Lagerstätte within the Winneshiek Shale is important because it represents an interval when exceptional preservation is rare. The biota includes the earliest eurypterid, a giant form, as well as a new basal chelicerate and the earliest ceratiocarid phyllocarid. Conodonts, some of giant size, occur as bedding plane assemblages. Bromalites and rarer elements, including a linguloid brachiopod and a probable jawless fish, are also present. Similar fossils occur in the coeval Ames impact structure in Oklahoma, demonstrating that meteorite craters represent a novel and under-recognized setting for Konservat- Lagerstätten.
    [Show full text]
  • Magyar Királyi Földtani Intézet (2006.)
    ' Copyright Magyar `llami Fldtani IntØzet (Geological Institute of Hungary), 2005 Minden jog fenntartva! All rights reserved! Lektorok Reviewers: BALLA ZOLTÁN, CSÁSZÁRGZA, HAAS JÁNOS, HORVÁTH ISTVÁN, JÁMBOR Á RON, KOVÁCS SÁNDOR, KUBOVICS IMRE, LESS GYRGY, LIEBE PÁL,VICZIÁN ISTVÁN Sorozatszerkesztı Serial editor: BALLA ZOLTÁN Szakszerkesztı Scientific editor: PIROS OLGA Mßszaki szerkesztı Technical editor: SIMONYI DEZS SzÆmtgØpes nyomdai elıkØsztØs DTP: PIROS OLGA, SIMONYI DEZS Bortterv Cover design: SIMONYI DEZS Kiadja a Magyar `llami Fldtani IntØzet Published by the Geological Institute of Hungary Felelıs kiad Responsible editor: KORDOS L`SZL Igazgat Director HU ISSN 03689751 3 Tartalom — Contents Működési jelentés — Activity Report HÁMOR GÉZA (1934–2007) . 7 JÁMBOR ÁRON (összeállító): Dr. Hámor Géza szakirodalmi munkássága . 8 KORDOS LÁSZLÓ: A múlt a jövő kulcsa . 17 BREZSNYÁNSZKY KÁROLY: Igazgatói beszámoló a Magyar Állami Földtani Intézet 2006. évi tevékenységéről . 19 Szakcikkek — Scientific publications RIPSZNÉ JUDIK KATALIN: A Medvednica hegység (Horvátország) és Észak-Magyarország paleozoos és mezozoos kishőmérsékletű metamorf képződményeinek összevetése. — Comparison of Palaeozoic and Mesozoic very low- grade metamorphic formations in the Medvednica Mts (Croatia) and in North Hungary. 47 PELIKÁN PÁL, IVAN FILIPOVIĆ, DIVNA JOVANOVIĆ, MILAN SUDAR, †LJUBINKO PROTIĆ, HIPS KINGA, KOVÁCS SÁNDOR, LESS GYÖRGY: A Bükki-terrénum (É-Magyarország), a Jadari-terrénum (ÉNy-Szerbia) és a Sana-Unai-terrénum (ÉNy-Bosznia) karbon, perm és triász rétegsorainak összehasonlítása. — Correlation of the Carboniferous, Permian and Triassic sequences of the Bükk, Jadar, Sana-Una terrains. 59 BUDAI TAMÁS: Platformok és medencék kialakulása és fejlődése a Bakony középső-triász története során. — Middle Triassic platform and basin evolution of the Bakony Mts, Hungary. 77 HAAS JÁNOS: A bükki és a darnói jura képződmények ősföldrajzi helyzete és kapcsolatai.
    [Show full text]
  • County of Riverside General Plan Reche Canyon/Badlands Area Plan
    County of Riverside General Plan Reche Canyon/Badlands Area Plan COUNTY OF RIVERSIDE Transportation and Land Management Agency 4080 Lemon Street, 12th Floor Riverside, CA 92501-3634 Phone: (951) 955-3200, Fax: (951) 955-1811 October 2011 County of Riverside General Plan Reche Canyon/Badlands Area Plan TABLE OF CONTENTS Vision Summary.......................................................................................................................................................... iv Introduction ................................................................................................................................................................. 1 A Special Note on Implementing the Vision ........................................................................................................ 2 Location ........................................................................................................................................................................ 3 Features ........................................................................................................................................................................ 7 Setting ....................................................................................................................................................................... 7 Unique Features ........................................................................................................................................................ 7 Badlands/Norton Younglove Preserve
    [Show full text]
  • Grand Canyon National Park Service U.S
    National Park Grand Canyon National Park Service U.S. Department of the Interior The Painted Map by Erwin Ralsz WHAT IS The Painted Desert is a well-known Formation. While several rock layers in THE PAINTED DESERT? Arizona landscape of very colorful "bad northeastern Arizona are colorful, it is the lands" extending across northeastern particular beauty of the Chinle Formation Arizona. (Badlands are intricately dis that gave rise to the notion of a Painted sected, barren, and rounded landscapes that Desert. Although the Chinle Formation can typically occur in arid regions where weak be seen elsewhere, in the Painted Desert the rock is prevalent). The Painted Desert is exposure of this rock is long and continu distinctly defined by exposures of a rock ous. layer known as the Chinle (Chin-lee) The Painted Desert is exposed in a of Winslow, Arizona along State Highway WHERE TO SEE band of rock trending northwest from 87. Winslow is 140 miles from Grand THE PAINTED DESERT Holbrook, Arizona to The Gap, Arizona. Canyon's South Rim. This band is wider in the Holbrook area and narrows significantly to the northwest. Few Closest to Grand Canyon, the Painted roads provide access to the Painted Desert. Desert is exposed in a narrow band along U.S. Highway 89 from about 3 miles north Unquestionably, the most famous part of Cameron, Arizona (at milepost#470) to of the Painted Desert is at Petrified Forest the small village of The Gap farther north. National Park, 190 miles from the South A small but visually striking example of the Rim of Grand Canyon.
    [Show full text]
  • The Cretaceous-Tertiary Boundary Interval in Badlands National Park, South Dakota
    The Cretaceous-Tertiary Boundary Interval in Badlands National Park, South Dakota Philip W. Stoffer1 Paula Messina John A. Chamberlain, Jr. Dennis O. Terry, Jr. U.S. Geological Survey Open-File Report 01-56 2001 U.S. DEPARTMENT OF THE INTERIOR Gale A. Norton, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director The Cretaceous/Tertiary (K-T) boundary study interval at the Rainbow Colors Overlook along Badlands Loop Road, North Unit of Badlands National Park. This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey (USGS) editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 1345 Middlefield Road, Menlo Park, CA 94025 http://geopubs.wr.usgs.gov/open-file/of01-056/ ABSTRACT A marine K-T boundary interval has been identified throughout the Badlands National Park region of South Dakota. Data from marine sediments suggest that deposits from two asteroid impacts (one close, one far away) may be preserved in the Badlands. These impact- generated deposits may represent late Maestrichtian events or possibly the terminal K-T event. Interpretation is supported by paleontological correlation, sequence stratigraphy, magnetostratigraphy, and strontium isotope geochronology. This research is founded on nearly a decade of NPS approved field work in Badlands National Park and a foundation of previously published data and interpretations. The K-T boundary occurs within
    [Show full text]
  • Introduction
    Introduction Introduction Doing Science Science & Society Our Environmental Heritage The Science of Global Change Summary The materials of science are the material of life itself. Science is part of the reality of living; it is the what, the how, and the why of everything in our experience. It is impossible to understand man without understanding his environment and the forces that have molded him physically and mentally. The aim of science is to discover and illuminate truth. Rachel Carson Whatever knowledge is attainable, must be obtained by scientific methods, and what science cannot discover, mankind cannot know. Bertrand Russell Introduction • Earth science, geology and environmental geology involve the study of the Earth and the processes that shape its surface but have different emphases. • The Earth System is composed of four principal components: atmosphere, hydrosphere, biosphere, and the solid Earth. • The science of Earth becomes relevant to society when we examine the interaction between human beings and the planet we share. The Good Earth represents an attempt to introduce students to Earth Science with an emphasis on our interaction with our environment. Consequently, this text includes components from two common undergraduate courses, Earth Science and Environmental Geology. These courses have more elements in common than they have differences. • Geology is the study of the Earth. That includes how the planet was formed, what it is made from, and how it has changed over time. Geologists study the processes that occur on Earth's surface and others taking place within the planet's interior. • Environmental geology views geology through the prism of the human experience.
    [Show full text]
  • Impact Structures and Events – a Nordic Perspective
    107 by Henning Dypvik1, Jüri Plado2, Claus Heinberg3, Eckart Håkansson4, Lauri J. Pesonen5, Birger Schmitz6, and Selen Raiskila5 Impact structures and events – a Nordic perspective 1 Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, NO 0316 Oslo, Norway. E-mail: [email protected] 2 Department of Geology, University of Tartu, Vanemuise 46, 51014 Tartu, Estonia. 3 Department of Environmental, Social and Spatial Change, Roskilde University, P.O. Box 260, DK-4000 Roskilde, Denmark. 4 Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen, Denmark. 5 Division of Geophysics, University of Helsinki, P.O. Box 64, FIN-00014 Helsinki, Finland. 6 Department of Geology, University of Lund, Sölvegatan 12, SE-22362 Lund, Sweden. Impact cratering is one of the fundamental processes in are the main reason that the Nordic countries are generally well- the formation of the Earth and our planetary system, as mapped. reflected, for example in the surfaces of Mars and the Impact craters came into the focus about 20 years ago and the interest among the Nordic communities has increased during recent Moon. The Earth has been covered by a comparable years. The small Kaalijärv structure of Estonia was the first impact number of impact scars, but due to active geological structure to be confirmed in northern Europe (Table 1; Figures 1 and processes, weathering, sea floor spreading etc, the num- 7). First described in 1794 (Rauch), the meteorite origin of the crater ber of preserved and recognized impact craters on the field (presently 9 craters) was proposed much later in 1919 (Kalju- Earth are limited.
    [Show full text]
  • GEOLOGIC MAP of the TERRY 30´ X 60´ QUADRANGLE EASTERN MONTANA
    GEOLOGIC MAP OF THE TERRY 30´ x 60´ QUADRANGLE EASTERN MONTANA Compiled and mapped by Susan M. Vuke1 and Roger B. Colton2 Montana Bureau of Mines and Geology Open File Report MBMG 477 2003 1Montana Bureau of Mines and Geology 2U.S. Geological Survey Map revised: 2007 This report has been reviewed for conformity with Montana Bureau of Mines and Geology technical and editorial standards. Partial support has been provided by the STATEMAP component of the National Cooperative Geologic Mapping Program of the U.S. Geological Survey under contract Number 02-HQ-AG0038. 107° 106° 105° 104° 47°30' Circle 200 Jordan 200s 200 GLENDIVE CIRCLE JORDAN 200s Glendive 94 47° 59 Wibaux Terry TERRY WIBAUX ANGELA 46°30' Miles City 12 Baker 12 Forsyth 94 MILES CITY BAKER FORSYTH 59 46° Location of Terry 30'x60' quadrangle and adjacent geologic maps published by MBMG. 1 CORRELATION DIAGRAM TERRY 30´ x 60´ QUADRANGLE Qal Holocene Qac Qls Qat Quaternary QTcl QTat Pleistocene Pliocene Tftr Tertiary Tfle Paleocene Tfld Tft Fort Union Formation Fort 2 DESCRIPTION OF MAP UNITS TERRY 30´ x 60´ QUADRANGLE Note: Thicknesses are given in feet because original field maps were on 7.5’ quadrangles with topographic contour intervals in feet. To convert feet to meters (the contour interval unit on this map), multiply feet x 0.3048. Qal ALLUVIUM (HOLOCENE)—Light-brown and gray, moderately to well-sorted and stratified clay, silt, sand and gravel. As much as 100 ft thick under floodplain of the Yellowstone River and as much as 25 ft thick under tributaries of the Yellowstone River.
    [Show full text]
  • Episodic Sediment Delivery and Landscape Connectivity in the Mancos Shale Badlands and Fremont River System, Utah, USA
    Geomorphology 102 (2008) 242–251 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph Episodic sediment delivery and landscape connectivity in the Mancos Shale badlands and Fremont River system, Utah, USA Andrew E. Godfrey 1, Benjamin L. Everitt a, José F. Martín Duque b,⁎ a 170 W. 300 North, Ivins, Utah 84738, USA b Department of Geodynamics, Complutense University, 28040 Madrid, Spain ARTICLE INFO ABSTRACT Article history: The Fremont River drains about 1000 km2 of Mancos Shale badlands, which provide a large percentage of the Accepted 23 May 2007 total sediment load of its middle and lower reaches. Factors controlling sediment movement include: Available online 18 May 2008 weathering that produces thin paralithic soils, mass movement events that move the soil onto locations susceptible to fluvial transport, intense precipitation events that move the sediment along rills and across Keywords: local pediments, and finally Fremont River floods that move the sediment to the main-stem Colorado River. Mancos Shale badlands A forty-year erosion-pin study has shown that down-slope creep moves the weathered shale crust an Erosion Mass movement average of 5.9 cm/yr. Weather records and our monitoring show that wet winters add large slab failures and Connectivity mudflows. Recent sediment-trap studies show that about 95% of sediment movement across pediments is Coupling accomplished by high-intensity summer convective storms. Between 1890 and 1910, a series of large autumn Arroyo cutting floods swept down the Fremont River, eroding its floodplain and transforming it from a narrow and meandering channel to a broad, braided one.
    [Show full text]
  • Basin/Badlands of Southwestern South Dakota
    222 RANGELANDS 18(6), December 1996 Black-footed Ferret Reintroduction in the Conata Basin/Badlands of Southwestern South Dakota Peter M. McDonald and Glenn E. Plumb he long, slender creature cautiously emerged from its footed ferrets are adapted to preying on prairie dogs for hole, glancing right, left, right again, then directly at food and using undergroundburrow systems of prairie dogs Tthe beam of the spotlight fixed on him. The emerald for shelter and family-rearing. green eyes glimmered in the powerful light like no other At one time, it would have been a superb strategy for the animal of the prairie could. or should. Forthese were the black-footedferret to exploit such an abundant and season- eyes of one of the rarest free-ranging mammals in the ally reliable source of food and shelter represented by world, certainly the rarest on the North American continent. prairie dog communities. Over 100 million acres of prairie And these eyesgazed out over the surrounding grasslands dog towns were dispersed across the Great Plains in the of the Conata Basin/Badlands region of southwestern late-nineteenthcentury. However, early settlers viewed the South Dakota for the first time in over thirty years. intensive burrowing and grazing disturbances by this colo- The black-footed ferret (Mustela nigripes) was first nial, native rodent as incompatiblewith agrarian land uses. described in 1851 by the legendary naturalist, John James Intensive efforts to chemically and mechanically eliminate Audubon, and John Bachman. A member of the weasel local prairie dog populationsgenerated an unforeseencon- family, the black-footed ferret has since been identified as sequence: massive reduction and fragmentation of the the only ferret native to North America.
    [Show full text]